This invention relates to a process for preparing a resistant granular starch with high dietary fiber content. More particularly, this invention involves the preparation of a resistant granular starch by the selected heat-moisture treatment of high amylose starch and further to the use of this resistant granular starch in food products.
Starch, a complex carbohydrate, is composed of two types of polysaccharide molecules, amylose, a mostly linear and flexible polymer of D-anhydroglucose units that are linked by alpha-1,4-D-glucosidic bonds, and amylopectin, a branched polymer of amylose chains that are linked by alpha-1,6-D-glucosidic bonds. Starch is digested predominantly in the small intestine by the enzyme alpha-amylase. Alpha-amylase hydrolyzes alpha-1,4-D-glucosidic bonds and therefore hydrolyzes the amylose fraction of starch almost completely to simple sugars. Alpha-amylase does not hydrolyze the alpha-1,6-D-glucosidic linkages, resulting in less complete hydrolysis of the amylopectin fraction.
It is known that certain starch processing operations result in the transformation of starch into starch that is resistant to amylase, known simply as resistant starch. Resistant starch is not digested by amylase in the small intestine, but passes into the large intestine where research literature indicates it behaves with properties similar to dietary fiber. Resistant starch, thus has reduced caloric value because it resists digestion and is likely to be a factor in prevention of diverticulosis and colon cancer.
Resistant starch (RS) has been classified in the literature into three categories: RS1--physically inaccessible starch (e.g., starch embedded in a protein or fiber matrix, such as starch found in a whole grain); RS2--intact digestion resistant native starch granules (e.g., uncooked potato or banana starch); and RS3--retrograded digestion resistant starch (see Englyst and Cummings, "New Developments in Dietary Fiber", Planum Press, NY 1990).
Various methods have been reported for producing resistant starch. Many of these methods involve the RS3 retrograded type described above, and this follows the general belief that resistant starch is formed when the amylose fraction of starch is retrograded or recrystallized after the gelatinization of starch. The theory is that the flexible linear amylose molecules align themselves after gelatinization into tight linear configurations that can form helices or spheres making many of the alpha-1,4-glucoside linkages inaccessible to alpha-amylase.
U.S. Pat. No. 5,051,271 issued Sep. 24, 1991 to R. Iyengar, et al. discloses a food grade, non-digestible, low-calorie bulking agent derived from starch and a process for producing it. The process involves retrogradation of starch, followed by enzymatic or chemical hydrolysis to reduce or remove the amorphous regions of the retrograded starch.
WO 90/15147 published Dec. 13, 1990 to Y. Pomeranz, et al. discloses a method for preparing purified resistant starch by cooling a cooked starch paste to form a gel, homogenizing the gel in water, digesting away the non-resistant portions with alpha-amylase, and drying the remaining unconverted portion under low temperature.
U.S Pat. No. 5,281,276 issued Jan. 25, 1994 to Chiu, et al. involves a process for producing resistant starch from high amylose starches by gelatinizing a starch slurry, enzymatically debranching the starch, and isolating the starch product by drying or extrusion.
All of the methods described above involve dispersing and gelatinizing starch in large excess amounts of water, followed by retrogradation and the use of enzymes or acids, resulting in RS3-type resistant starch. These methods can be laborious, time consuming and result in low yields and the high water content leads to a costly drying step.
Native starch granules have some crystallinity and are known to be partially resistant to enzyme digestion. It is also known that heat treatment can change the properties of starch. However, no disclosure has been made for the preparation of resistant granular starch with high total dietary fiber content from high amylose starch.